1. Field
This specification relates to medical imaging systems and processes. In particular, the present invention relates to the computer aided detection of breast malignancies, and devices and methods of interactive display of computer aided detection results in combination with quantitative prompts.
2. Related Art
Current systems for computer aided detection (CAD) are aimed at avoiding that radiologists miss abnormalities due to perceptual oversights during a radiological screening examination. In these systems potentially abnormal patterns identified by computer programs are displayed after the reader has inspected a screening case. Readers are encouraged to evaluate regions marked by CAD in addition to the ones they identified themselves as suspicious. On the other hand, decisions with respect to regions they already inspected are not to be changed.
A second source of observer errors in radiological screening is related to misinterpretation of detected abnormalities. However, this type of error is not addressed in current CAD prompting systems. In previous work it has been shown that there is a potential to use current CAD systems for improvement of interpretation of mammographic masses. See, N. Karssemeijer, J. D. Otten, A. L. Verbeek, J. H. Groenewoud, H. J. de Koning, J. H. Hendriks, and R. Holland. Computer-aided detection versus independent double reading of masses on mammograms. Radiology, 227(1): 192-200, 2003. In fact, if analysis is restricted to regions that are considered suspicious by radiologists, malignancy ratings of a CAD system were shown to be comparable in quality to assessments of experienced radiologists. See, N. Karssemeijer, J. D. Often, H. Rijken, and R. Holland. Computer aided detection of masses in mammograms as decision support. Br J Radiol, 79 Spec No 2:S123-6, 2006. Therefore, combining CAD ratings with radiologists' assessments can lead to significant improved detection performance, and that this improvement may be comparable to that obtained by independent double reading. See, Id.
However, independent combination of CAD ratings with reader scores is not likely to become accepted in screening practice. Moreover, it may be expected that readers will benefit more from CAD can if they learn to use it interactively. See, N Karssemeijer, A Hupse, M Samulski, M Kallenberg, C Boetes, and G den Heeten. An interactive computer aided decision support system for detection of masses in mammograms. In E A Krupinski, editor, Digital Mammography, LNCS 5116, pages 273-278, 2008, hereinafter “Digital Mammography 2008.” This is especially true if they are aware of the limitations of the CAD system.
A third source of observer errors in radiological screening is a lack of quantitative matrix or guideline to determine which patient should be recalled for a more in-depth “diagnostic” examination. The current standard BIRADS system, used in radiological examinations, supplies a guideline specifying that no recall is necessary for “probably benign” cases, or BIRADS category III cases. It further specifies that these BIRADS III cases have a risk of malignancy below 2% (two percent), but it gives no quantitative guideline on how to assess that a lesion is below 2% in probability of malignancy. This vagueness results in a wide specificity range in the practice of radiologists in making recalls during screening. For example, see the report by Yankaskas et al, in American Journal of Roentgenology 2001, vol. 177, pages 543-549, entitled “Association of Recall Rates with Sensitivity and Positive Predictive Values of Screening Mammography”, of a study included 215,665 mammograms. The reported specificity varied from 86.6% (or 13.4% recall) to 98.1% (1.9% recall). The low specificity would result in substantially increased healthcare costs and increased anxiety in recalled patients. However, this source of errors is not addressed in current CAD prompting systems.
U.S. Application Publication No. 2004/0184644 discusses a display for computer aided evaluation of medical images in the diagnostic phase rather than at the screening phase. Also, although a method is described as displaying a likelihood of malignancy, the likelihood appears to be relative only and there is no discussion of calibration to absolute or quantitative probabilities.